1. Field of Invention
The invention relates to a method for the automatic closing of transport bags after filling with a bulk material, according to the pre-characterizing clause of claim 1, and to an apparatus for carrying out the method.
The method according to the invention and the associated apparatus are used particularly in the bagging and closing of transport bags (preferably paper bags) for large packs (approximately 10-50 kg) of meals, fodders and the like.
2. Description of Related Art
The closing of small consumer packs of up to approximately 2 kg is usually carried out in high-performance automatic packaging machines. Because of the smallness of the masses to be moved and of the paper areas, the cycles of movement can be executed at high speed, thus allowing very high performances.
In contrast, large packs having masses greater than 5 kg require completely different handling. The transport bags often used for these can have a mass of up to 50 kg and more. Even when some tendency towards smaller packs can be observed, the masses to be moved, the unstable type of package and the sheet-like bag parts allow only comparatively low accelerations. Excessive accelerations would damage the bag material or would deform the package, together with the orifice, in such a way, that it becomes useless for subsequent work steps.
Although, in so-called valve bags, closing presents relatively little problem on account of the filling orifice which can be closed in a valve-like manner, nevertheless, for reasons of bagging capacity, the empty-bag price and sanitation, they are used to only a qualified extent for foodstuffs and fodders.
Foodstuffs and fodders, especially also ground materials, require a leakproof closing of the transport bag in both directions. Neither should the filling material escape from the bag, nor should moisture, harmful substances or insects penetrate. The transport bags must be closed carefully by sewing (holes, perforation) or preferably by glueing/adhesive bonding.
Also, even small differences in density of the bag content result in differences in the degree of filling. Since, in the non-closed state, a transport bag does not have any exactly defined cubic dimensions, its automated handling and palletization present problems. Each bag must nevertheless be shaped uniformly and should also not include any air cushions, in order to produce a transportable bag stack (palletization). It is therefore impossible, for example, to wish to increase merely the degree of mechanization of a bag-closing apparatus. In addition, there are widely varying batch sizes which necessitate a frequent conversion of the apparatus.
At the same time, there are also limits on sewing which is widely used. The sewing speed cannot be increased arbitrarily, and bags made of thin material (weight reduction) cannot be sewn so as to be leakproof and tend to tear. The glueing/adhesive bonding of the bags constitutes a basic solution.
In a filled and non-spread transport bag, the position of the edges of the bag orifice can vary greatly, this making exact sewing or glueing difficult. It is, for example, necessary and known, for an exact folding operation, to cut off a strip from the upper bag edge, in order to obtain an accurate horizontal and vertical position of the latter. However, such a solution necessitates an additional mechanical outlay and the disposal of the cut-off material. To mitigate these disadvantages, it is proposed, for example in EP-A-293,615, for the closing of side-folding bags made of paper, to grasp the filled bag directly in the filling station in a clamping manner and to move it into the subsequent folding station by means of a slide. A disadvantage of this version, which is simple per se, is the fact that, although the open bag end can be grasped relatively accurately, the preshaped structure can nevertheless often be received only with great inaccuracy.
According to EP-A-123,784, it is proposed, before folding, to detach a paper layer by a few centimeters and subsequently to glue the tab thus formed as a protective tab directly, via the folding point, to a point on the bag material which is located outside the folding point. This can afford an additional safeguard of the bag closure against peeling open, even when the adhesive bond is not made in the best possible way. Here too, a disadvantage is a complication of the folding operation which, particularly in the case of a high plant capacity, can impair reliability. Moreover, use is possible only in the case of multi-layer paper.
A similar solution is described in DE-A-2,520,744, the operator's choice of bag material being restricted by a special bag make-up.